Variations of plant N, P concentrations in shrubland biomes across northern China: Phylogeny, climate and soil
Nitrogen (N) and phosphorous (P) are essential macroelements for plants and play critical roles in plant survival and growth. Most of previous plant studies on N and P related stoichiometry have biased towards forests and grasslands. Exploring stoichiometry patterns of shrubs is needed to fully understand the macroecological patterns in plant stoichiometry and driving factors. In this study, we examined the patterns of leaf N and P concentrations and the allocation strategies of N and P in different plant organs, based on samples of soil and shrub species from 361 sites across Northern China. We explored the effects of climate, soil nutrients, and plant evolutionary history on these patterns and strategies.
Leaf N and P concentrations responded to environment and phylogeny in different ways. Leaf N concentration was more phylogenetically conserved, and was less influenced by environmental factors than leaf P. Nevertheless, leaf N concentration was significantly affected by precipitation, whereas leaf P concentration was jointly influenced by soil nutrients and climate. At the community level, climate and soil nutrients influenced plant chemical traits in different ways. Climate influenced the community chemical traits through shift in species composition, whereas soil influenced the community chemical traits directly by changing N and P concentrations of individual species.
N and P concentrations also showed different scaling relationships among plant organs, which could be attributed to the different requirements of N and P among organs for performing various functions. The scaling relationships of N concentration across different plant organs tended to be allometric between leaves and non-leaf organs, and isometric between non-leaf organs. Whilst the scaling relationships of P concentration tended to be allometric for root vs. stem and for root vs. leaf, the relationship tended to be isometric for stem vs. leaf. Plants’ nutrient allocation strategies among organs were affected by aridity, but not by soil nutrient concentration or plant evolutionary history. In arid environments, plants tend to have higher N concentration in leaves at given root or stem N concentration.